1 /*
2 * Copyright 2011 Tilera Corporation. All Rights Reserved.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation, version 2.
7 *
8 * This program is distributed in the hope that it will be useful, but
9 * WITHOUT ANY WARRANTY; without even the implied warranty of
10 * MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE, GOOD TITLE or
11 * NON INFRINGEMENT. See the GNU General Public License for
12 * more details.
13 */
14
15 #include <linux/types.h>
16 #include <linux/string.h>
17 #include <linux/module.h>
18
memchr(const void * s,int c,size_t n)19 void *memchr(const void *s, int c, size_t n)
20 {
21 const uint64_t *last_word_ptr;
22 const uint64_t *p;
23 const char *last_byte_ptr;
24 uintptr_t s_int;
25 uint64_t goal, before_mask, v, bits;
26 char *ret;
27
28 if (__builtin_expect(n == 0, 0)) {
29 /* Don't dereference any memory if the array is empty. */
30 return NULL;
31 }
32
33 /* Get an aligned pointer. */
34 s_int = (uintptr_t) s;
35 p = (const uint64_t *)(s_int & -8);
36
37 /* Create eight copies of the byte for which we are looking. */
38 goal = 0x0101010101010101ULL * (uint8_t) c;
39
40 /* Read the first word, but munge it so that bytes before the array
41 * will not match goal.
42 *
43 * Note that this shift count expression works because we know
44 * shift counts are taken mod 64.
45 */
46 before_mask = (1ULL << (s_int << 3)) - 1;
47 v = (*p | before_mask) ^ (goal & before_mask);
48
49 /* Compute the address of the last byte. */
50 last_byte_ptr = (const char *)s + n - 1;
51
52 /* Compute the address of the word containing the last byte. */
53 last_word_ptr = (const uint64_t *)((uintptr_t) last_byte_ptr & -8);
54
55 while ((bits = __insn_v1cmpeq(v, goal)) == 0) {
56 if (__builtin_expect(p == last_word_ptr, 0)) {
57 /* We already read the last word in the array,
58 * so give up.
59 */
60 return NULL;
61 }
62 v = *++p;
63 }
64
65 /* We found a match, but it might be in a byte past the end
66 * of the array.
67 */
68 ret = ((char *)p) + (__insn_ctz(bits) >> 3);
69 return (ret <= last_byte_ptr) ? ret : NULL;
70 }
71 EXPORT_SYMBOL(memchr);
72